Field of the Invention
Internal combustion engines operate under a wide range of temperatures including low-temperature stop-and-go service as well as high temperature conditions produced by continuous high speed driving. Stop-and-go driving, particularly during cold, damp weather conditions, leads to the formation of sludge in the crankcase and oil passages of a gasoline engine. This sludge seriously limits the ability of the crankcase oil to lubricate the engine. In addition, the sludge tends to contribute to rust formation within the engine. The noted problems are compounded by lubrication service maintenance recommendations calling for extended oil drain intervals.
It is known to employ nitrogen-containing dispersants and/or detergents in the formulation of crankcase lubricating oil compositions. Many of the known dispersant/detergent compounds are based on the reaction of an alkenylsuccinic acid or anhydride with an amine or polyamine to produce an alkenylsuccinimide or an alkyenylsuccinamic acid as determined by selected conditions of reaction.
It is also known to chlorinate alkenylsuccinic acid or anhydride prior to the reaction with an amine or polyamine in order to produce a reaction product in which a portion of the amine or polyamine is attached directly to the alkenyl radical of the alkenylsuccinic acid or anhydride. The thrust of many of these processes is to produce a dispersant having a relatively high level of nitrogen. The noted known processes generally result in the production of a dispersant reaction product typically containing from about 0.5 to 5% nitrogen. These dispersant additives exhibited a high degree of oil solubility and have been found to be effective for dispersing the sludge that is formed under severe low temperature stop-and-go engine operating conditions. However, it has become increasingly difficult to formulate lubricants with these additives which meet the present requirements with respect to the prevention or inhibition of the formation of varnish.